Field of the Invention
The invention relates to a switching stage having a differential amplifier configuration, a first bipolar transistor being connected as an emitter follower circuit to an output of the differential amplifier configuration and having an emitter being connected to an output of the switching stage, a current source connected between the output of the switching stage and a terminal for a supply potential, a second bipolar transistor being connected as an emitter follower circuit to the output of the differential amplifier configuration, the emitter of the first bipolar transistor being connected to a first input of a comparison device and the emitter of the second bipolar transistor being connected to a second input of the comparison device, the current source being a controllable current source with a control input connected to an output of the comparison device, and the controllable current source being controlled by the comparison device in such a way that a high current is impressed by the current source if the potential of the emitter of the first bipolar transistor is higher than the potential of the emitter of the second bipolar transistor, and otherwise a low current being impressed. One such switching stage is known from Published European Application No. 0 367 612 A2 and is shown in FIG. 1 in the form of a basic circuit diagram. In the known switching stage, the comparison device is provided by means of a differential amplifier which is formed with two transistors having emitters that are connected to reference potential through a current source. The controllable current source has a two-stage structure.
Published European Application No. 0 438 953 A1 also discloses a switching stage having a differential amplifier, two bipolar transistors, and a comparison circuit that triggers a current source and is constructed as a current mirror circuit. In that switching stage, however, the two bipolar transistors are triggered by differential amplifier outputs of different polarity.
Patents Abstracts of Japan No. 2-231814 (A), 1990, Vol. 14, No. 541, E-1007, also discloses a switching stage having a differential amplifier, two bipolar transistors, and a comparison circuit that triggers a current source. That comparison circuit is formed by a two-stage current switch. Once again, the bipolar transistors are each triggered by a different output of the differential amplifier.